This invention relates to analytical instruments and methods. In one aspect, it relates to the analysis of a hydrocarbon sample to determine the isotopic carbon content. In another aspect, the invention relates to methods and instruments for geochemical oil prospecting.
Modern methods of oil exploration involve the use of a combination of seismic and geochemical prospecting methods. Geochemical prospecting methods have developed from an understanding of the ways in which petroleum originated and relocated in, or migrated to, a particular location. It is known that petroleum has an organic origin and developed from the remains of living organisms deposited into sediments. The sediments were buried and the action of temperature and pressure over time generated petroleum from the deposited organic matter. It is believed that petroleum found in reservoirs today has often migrated to the reservoir from the original location of petroleum generation.
In exploring for oil, it is useful to know the locations of such oil-generating formations, which can then be used in combination with seismic and geological data from the region to predict the locations of other oil-bearing reservoirs to which oil may have migrated from a common source formation. If information on the type of source rock can be obtained from petroleum or other type of geological sample, this information can be used in finding the source formation and in targeting future drilling at this formation and proximal traps. In addition, assessment of source rock type from known reservoir samples can enable determination of whether a common source for the reservoirs is involved. Different sources may indicate possible additional undiscovered reservoirs in proximal locations.
One geochemical oil prospecting method involves the study of carbon-containing geological samples from an oil-bearing region to determine the relative amounts of carbon isotopes in the sample. In such a method, it is common to convert the carbon in the sample to carbon dioxide and then to measure by means of an isotope ratio mass spectrometer or other instrument the ratio of C.sup.13 to C.sup.12 in the sample.
It is thus important to be able to quantitatively convert the carbon in a sample to carbon dioxide. This can be done by combustion of the sample in an oxygen-rich atmosphere. For the type of geochemical methods which are presently used to study samples, it is desirable to study the carbon isotopic ratio of relatively small samples, say on the order of 2 cubic centimeters. Conventional methods for such an analysis, however, require relatively large samples in the order of 50 to 100 cc to produce accurate, reproducible results. The use of such large samples has the disadvantages of requiring a relatively long time to run an analysis, of requiring amounts of samples of material which are sometimes difficult to obtain or retain, and requiring large combustion apparatus in addition to the mass spectrometer. Certain conventional instruments also produce inconsistent results due to incomplete conversion of carbon to carbon dioxide.
It is therefore an object of this invention to provide apparatus and method for analyzing a sample of matter.
It is a further object to provide a simple and rapid method for determining the isotopic carbon ratio of a hydrocarbon sample.
It is a further object to provide means for determining the source rock potential of a geological sample.